The cresol isomers are in substantial demand for various applications in the manufacture of phenolic resins, plasticizers, inhibitors, agricultural chemicals, ore flotation chemicals, germicides, antiseptics and disinfectants. The use varies with the particular isomer. For example, para-cresol is particularly useful in disinfectants or fumigating compositions, in production of cresotimic acid, dye stuffs and organic intermediates.
Meta-cresol is particularly useful as a disinfectant, fumigating compositions, photographic chemicals, ore flotation chemicals, paint and varnish removers, in the production of synthetic resins, explosives and organic chemicals.
Furthermore, applications for intermediates or final products utilizing a purified mixture of para- and meta-cresol exist, especially in the commercially important butylation of mixed m- and p-cresols. Previous adsorptive separation processes were suitable for extracting the para-cresol isomer from meta- and ortho-cresol, but effective processes for separating both para- and meta-cresol were not available.
Adsorptive processes for separating cresol isomers have been previously known, e.g., from U.S. Pat. Nos. 3,014,078; 3,969,422 and 4,356,331. Also the separation of xylenols from cresols with adsorbents is known, for example, from U.S. Pat. Nos. 4,124,770 and 4,386,225.
More specifically, U.S. Pat. No. 3,014,078 teaches the separation of cresol isomers by employing an adsorbent consisting of an X-type zeolite exchanged with calcium, barium, etc., to selectively adsorb cresol from a cresol isomer feed mixture thereby producing a rich adsorbent. In the preferred mode of operation, the adsorbed isomer is then removed by contacting with a displacement exchange fluid. A preferred displacement exchange fluid is phenol although other materials which may be employed include ethers, aromatic hydrocarbons, and paraffin hydrocarbons.
U.S. Pat. No. 4,356,331 discloses a process for selectively adsorbing an alkyl phenol isomer onto a potassium exchanged Y zeolite, preferably also containing an additional cation, e.g., strontium or barium and subsequently desorbing the selectively adsorbed isomer with an aliphatic ketone desorbent. This patent disclosure is directed specifically to the separation of p-cresol from m-cresol and contains no suggestion of applicant's separation.
U.S. Pat. No. 3,969,422 to Neuzil et al discloses a process for separating para-cresol from at least one other cresol isomer, especially meta-cresol, with the preferred adsorbent being barium-potassium exchanged X zeolite and the preferred desorbent being a saturated alcohol from 1 to 7 carbon atoms per molecule. Likewise, there is no disclosure of applicant's co-extraction of meta- and para-cresol from mixtures of ortho-cresol and other alkyl phenols.
The separation of xylenols from cresols with X or Y zeolites exchanged with various cations or mixtures thereof, e.g., potassium and barium, and alcohols as desorbents was discused in Neuzil Patent 4,386,225 and U.S. Pat. No. 4,124,770. In both patents containing similar disclosures all cresol isomers are extracted to substantially exclude the xylenol, which is collected in the raffinate. No disclosure of the critical role of water in the invention is contained in either patent.
The present invention relates to an improved process for separating the cresol isomers, by which high purity products of both para-cresol and meta-cresol can be obtained. In particular, we have found that by employing a particular adsorbent material, a co-extract of meta- and para-cresol can be obtained which can be subsequently separated into pure fractions of the individual isomers, meta-cresol and para-cresol, e.g., by a second stage adsorption process utilizing the same adsorbent and desorbent. Both products are valuable and therefore the ability to obtain highly pure fractions of each of the isomers of cresol is desirable.
It is also known that crystalline aluminosilicates or zeolites are used in adsorption separations of various mixtures in the form of agglomerates having high physical strength and attrition resistance. Methods for forming the crystalline powders into such agglomerates include the addition of an inorganic binder, generally a clay comprising a silicon dioxide and aluminum oxide, to the high purity zeolite powder in wet mixture. The blended clay zeolite mixture is extruded into cylindrical type pellets or formed into beads which are subsequently calcined in order to convert the clay to an amorphous binder of considerable mechanical strength. As binders, clay of the kaolin type or silica are generally used.
The invention herein can be practiced in fixed or moving adsorbent bed systems or in cocurrent, pulsed batch systems described in U.S. Pat. No. 4,159,284 or in cocurrent continuous simulated moving bed systems like that disclosed in Gerhold Patents 4,402,832 and 4,478,721, but the preferred system for this separation is a countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. Nos. 3,040,777 and 3,422,848. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRosset U.S. Pat. No. 3,706,812) to commercial scale in flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, but for reference thereto, Zinnen et al U.S. Pat. No. 4,642,397 is incorporated herein.